"Lastly, we must also point out that the more optimizations with sizeable effects that can be incorporated in a compiler, the poorer its original version must have been. In this connection, the cumbersome structures of many commercial compilers, whose origin is difficult to fathom, lead to surprisingly poor initial performance, which makes optimizing features seem absolutely indispensible." [1]

The "General Considerations" on page 100 is worth reading for its taxonomy of optimizations and point of view on optimizations.

Erick

[1] Compiler Construction, Nicolas Wirth, http://www-old.oberon.ethz.ch/WirthPubl/CBEAll.pdf